1. Field of the Invention
Embodiments of the invention generally relate to profile control for electroprocessing substrates.
2. Description of the Related Art
Electrochemical Mechanical Polishing (Ecmp) is a technique used to remove conductive materials from a substrate surface by electrochemical dissolution while concurrently polishing the substrate with reduced mechanical abrasion as compared to conventional Chemical Mechanical Polishing (CMP) processes. Electrochemical dissolution is performed by applying a bias between a cathode and a substrate surface to remove conductive materials from the substrate surface into a surrounding electrolyte. The bias may be applied to the substrate surface by a conductive contact disposed on or through a polishing material upon which the substrate is processed. A mechanical component of the polishing process is performed by providing relative motion between the substrate and the polishing material that enhances the removal of the conductive material from the substrate.
Profile control in some electroprocessing apparatuses has been generally realized by creating a plurality of process cells or zones across the width of the substrate being processed. By controlling the electrical bias or current flow between the individual cells, the rate of removal or deposition of conductive material on the substrate may be controlled.
However, control of the processing rate at the edge of the substrate has presented a significant challenge. As the electric potential of the electrolyte adjacent to the substrate has a greater (more negative) potential relative to the electrolyte located between the substrate and the electrode that defines a process cell, the voltage gradient is high at the edge of the substrate. The high voltage gradient causes greater current densities, and thus faster processing, at the edge of the substrate. Fast edge processing is generally undesirable because of the resulting reduction in usable substrate area for device fabrication. Thus, it would be desirable to improve profile control of an electroprocess such that the area near the edge of the substrate would have material removal and deposition rates comparable to the center of the substrate.
Thus, there is a need for an improved method and apparatus for electroprocessing.